Analysis CO₂ and Particulate Matter Meter DM306 / WS1125

What's so special about the DM306 CO₂ and particulate matter meter, you may ask, that I should review it, you ask?

On one of my long walks through AliExpress, I came across a very inexpensive CO2 and particulate matter meter, which I had seen many times before, but which I had already seen in the past. there was something that struck me this time that really caught my attention: they were selling it on the official Winsen website.

Winsen is an old acquaintance of mine and of the regular users of this blog. It is the manufacturer of the CO₂ sensor MH-Z19 with which I built the first home CO2 meter with wifi more than five years ago, on which the original home CO2 meter published in this blog was based (although after a short time I started recommending another similar sensor).

This manufacturer has a good reputationas it manufactures sensors from a more than acceptable quality at an economical price.

What captured my attention in this meter was its price. About 40 € for the version with CO2 meter only and 50 € for the version with CO2 and particle meter. in suspension PM1.0 PM 2.5 and PM10.

Of course, bearing in mind that only one CO2 sensor from this manufacturer costs about 18€ and a particulate sensor about 17€.For an additional 15 euros we were offered a finished commercial device, with a display of a very acceptable size and easy to read, rechargeable battery, audible alarm and all in a nicely designed box.

I immediately thought: "I have to buy one, find out what's inside and see if it's useful for our caching"..

Said and done, in less than 10 days I had it at home.

In this article I will tell you the following:

1. Unboxing of the meter: What the buyer actually receives, what is included in the box, and first impressions.
2. Analysis of the meter: How does it work in general, how about its battery, charging time and autonomy, how about its accuracy and precision, can we rely on its measurements?
3. "TeardownWhat components is it made of?
4. Reverse engineeringAnalysis and reverse engineering of its operation, protocols of its sensors, etc.

There is a fifth part which is my favourite, but you'll have to wait until I finish it to see it. Ehe hackingThe fun part: Will we be able to do a "The fun part!eMariewinsenstein"Will we be able to improve it and give it additional functionalities? I'm finishing it. You can't miss it!

Unboxing of the Wins DM306C or WS1125

The first thing I will tell you is that it is not at all clear what its name or manufacturer is, really.. On the outside of the box there is absolutely nothing about it, no manufacturer, no model, nothing. Clearly, a product to be sold massively through multiple brands.

The only indications on the box are: "Air Quality Monitor" on the top, "MADE IN CHINA" on the side and a few logos for certifications and environmental information. Nothing else.

Not even the manual says anything about the manufacturer or the model.. Only "Air Quality Monitor Instruction Manual".

Winsen apparently gives it the name of model WS1125 but many other sellers give it the name DM306 or DM306C and even its printed circuit board is engraved with ".DM306G_RB".

In Spain it is sold on Amazon with Tackly brandspecifically as TACKLY-03, and its description is "Tackly Ambient Co2 Meter"..

The truth is that, at this stage, not surprising at allas this is a way of acting very common in Chinese electronic products from low price (and quality).

The box comes with a scuff on one corner, as if it had been dragged across the tarmac from China to Madrid. But as comes fairly well packaged (a strong plastic envelope, lined with packing tape and several layers of bubble wrap) and the cardboard of the box is very hard, no major problems and the content is intact.

Inside the box we find the meter, encased in a custom-made plastic so that it does not move in the box, a micro USB cable and a short manual in English(Thank goodness it's not in Chinese!).

The meter housing is made of a fairly standard white plasticwith a pleasant design that reminiscent of a clock radio and prevents it from looking like a square piece of junk and helps it to look good anywhere.

When switched off, the screen looks quite generous, we'll see how it looks when switched on. It comes with one of those self-adhesive protection films to prevent scratching.

By the way, speaking of clock radios, the screen is a rather curious LCD type with a soft side illumination that makes it unobtrusive if you have it on your bedside table while you sleep.

Analysis of CO2 and Particulate Matter Meter DM306

The moment of truth arrives, the moment to turn it on.

I connect it with a mobile phone charger (not included) to its micro USB connector, press the only button on the device, and the meter turns on with a side-illuminated display with large characters and a very clear view.

In the first few seconds it gives us some meaningless measured beads and, after a few seconds, it starts to give us more realistic measurements..

It does not take long to stabilise and give values "logics". Maybe a minute.

As the measurement rises, towards stabilisation, the meter begins to emit a insistent 'beep' every few seconds. I check this brief manual and I see that The meter has an audible warning when 1000 ppm is reached..

The manual states that by double-clicking on the button on the front you can enable and disable the audible warning.. Like there is no indication on the display whether the audible warnings are active or not, so I have to make a few double-click attempts with different press speeds and cadences in between until, at last, the warnings stop. Finally it consisted of making two quick presses on that one button.

Incidentally, the threshold for activation the audible alarm is fixed at 1000 ppm without the possibility of changing this value. A pity.

CO2 measurements are somewhat lower than those of my other meters.. At low concentrations, the differences are above 50 - 100 ppm and at higher concentrations (above 1500 - 2000 ppm) the differences go up to 100 - 200 ppm.

Even if there is some deviation, the measurements seem to me to be sufficiently correct for a device of such a low price.. Let's think about what this device actually does: it can detect 400 CO₂ molecules in a million molecules of air. That seems to me to have a lot of merit.

Would a device be advisable to know the exact CO₂ concentration? Probably not a suitable meter to know the amount of CO2 in the environment very accurately.The CO2 concentration of the CO2, but it should be borne in mind that what we normally want is to have "an idea" of the relative changes in CO2, especially at the lower concentrations, and for this it is adequate and does a good job.

In other words, at concentrations below 1000 ppm (which are the ones we are most interested in) the reliability of the measurement is sufficient to know that we are "between 400 and 500 ppm" or "between 600 and 700 ppm". This is sufficient on the vast majority of occasions.

In addition to the CO2 concentration measurement, which is shown in larger characters and with more prominence on the display, the data from the particulate matter meter appears.

The meter provides data on the quantity of particles in suspension in the air at any given moment, updating this value every few seconds and separating them by different particle sizes.

This meter provides data on PM1, PM2.5 and PM10 particles.which are the standard values (particle sizes) commonly used for the measurement of this type of suspended "dust".

In order not to take up too much space on the screen, and to give more prominence to the CO₂, the different particle measurements PM1, PM2.5 and PM10 are shown in the following table. are appearing in successionevery few seconds, one after the other.

Speaking of the accuracy of the measurements, one thing that really struck me (accustomed, as I am, to analysing the technical data of many CO₂ sensors for our projects) was that precision data is nowhere to be found.

The accuracy data of the CO2 meter has been swallowed up by the earth.. Neither in the advertisement, nor in the manual, nor on the box, nor on the Winsen website.... nowhere does it tell us anything about it.

This lack of technical information from the manufacturer is already an indication that this is not a high-precision device.

In the tests I have done, CO₂ concentration accuracy has been lower than the other sensors I use. (Senseair S8 LP, which I use as a reference sensor, Senseair Sunrise S11, Winsen MH-Z19A, Winsen MH-Z19B, Winsen MH-Z19C, Netamo, Cubic CM1106SL-NS and other older Cubic models).

PM1, PM2.5 and PM10?

PM1, PM2.5 and PM10 is how the meters refer to the different sizes of airborne particles. PM1 is 1 μg (microgram or millionth of a gram, a very small measurement indeed), PM2.5 is 2.5 μg and PM10, yes that's right, 10 μg.

The meter tells us how many micrograms of each of these three particle sizes are in the air per cubic metre.

In this case I can't tell you anything about the accuracy of the measurements, as I don't have such an instrument to compare it with, although later I will tell you about the sensor it incorporates and I will be able to make some estimates..

The meter also includes environmental temperature and humidity sensors. I think it is very successful, given the target market, and complements the air quality data very well.

The tests I have carried out on the accuracy of temperature and relative humidity have been quite acceptableThis is particularly true given that most devices of this type are generally not very accurate.

In my office I have, due to all the projects and tinkering I do, many temperature and relative humidity sensors, starting with the quite accurate sensors of a Davis Vantage Pro 2 weather station, and continuing with sensors from Oregon Scientific, Digoo, Texas Instruments 18DS20, Bosch BME280, DHT22 and others. This allows me to make averages between them that are supposed to give me figures that are pretty close to reality. The temperature has been maintained within 1°C of each other and the relative humidity at approximately 5%.which is not bad at all.

In terms of controls, the meter is equipped with a single buttonThe button on the front panel allows you to turn it on with a short press, turn it off with a long press, switch between Celsius and Fahrenheit with a press when it is on, turn the pedidor off by holding the button down for a few seconds and activate and deactivate the alarm with two short, quick presses.

There are no other options. No calibration options, historical graphs or menu of any kind.

The meter is equipped with a rechargeable 2000 mAh lithium-ion battery. which gives it about 8 hours of autonomy (in my charging tests I have been able to verify that the reality is very close to this value, with more than 1900 mAh of charge).

I measured the full charge time at just over three hours. and a half, although observing the evolution of the charging current, I have been able to verify that it reaches a respectable charge (say the 80%) in considerably less time.

Autonomy is not bad at all for a meter which, let's not forget, measures not only CO₂ but also particulate matter (which is done by a technology which tends to have a high relative consumption).

My conclusion from the analysis

It is not a precision devicebut its low price makes it quite interesting for people who want a device to get an idea of how much CO2 is in the air and to be able to ventilate. I don't think that's its market either.

Logically There are more accurate devices, but they are also much more expensive. (especially if, like this one, they also have a particle sensor).

The fact that it includes a battery is also very interesting, and I would even say surprising, given the price of the meter. Its autonomy is more than enough for a day of measurements. using the meter as a portable.

On the plus side, the battery is a completely standard 18650 type, so we can replace it relatively easily if it goes bad, even though it is soldered in and the plastic lid is glued and it is not easy to open.